Changes in chromatin organization, meiotic status and the acquisition of meiotic competence in oocytes retained within mouse ovarian follicles for 0-6 days in culture were examined. Preantral follicles from 22-24 day old (prepubertal) mice develop antra and undergo significant growth from 0-4 days in culture after which the growth rates slow down. Oocyte meiotic status was evaluated by chromatin organization at day 0 and day 6 of follicle culture and the effects of a 24 hour exposure to LH during the last day of culture were determined. In prepubertal mice, meiotic arrest was maintained after 6 days and the majority of germinal vesicles (GVs) exhibited a transition from unrimmed to rimmed nucleoli. LH caused meiotic progression of intrafollicular oocytes. The transition from rimmed to unrimmed GV stages occurred between days 2 and 4 of follicle culture and was not influenced by exposure to LH. LH treatment, however did cause an increase in the proportion of intrafollicular oocytes resuming meiosis. Assays of meiotic competence in oocytes retrieved from cultured follicles demonstrated that the transition from an unrimmed to a rimmed state at day 3 to day 4 of culture is strongly correlated.